The invention relates to a method for use in association with an implanted medical device, particularly a device for performing cardiac pacing, defibrillation, cardioversion and the like. Such devices require the concurrent observation and interpretation of intracardiac electrogram (IEGM) signals that are obtained from multiple cardiac chambers. The method of the invention involves a signal, processing technique for reducing the interference of the signals.
The existence and use of implanted medical devices to conduct cardiac electrotherapy, including, for illustrative purposes, cardiac pacing, defibrillation, cardioversion and the like, is well-known. These devices rely upon a reliable technique for monitoring and analyzing the underlying electrical activity of the heart, as it is precisely this activity which may be therapeutically affected by the device. In the majority of these devices, the device receives signals from more than one of the cardiac chambers. Proper monitoring and analysis can be greatly enhanced if a single signal may be considered the exclusive representation of activity in the chamber from which the signal is detected. In other words, it is highly desirable to be able to consider a detected signal as being indicative of “near field” electrical activity.
In actual practice, the signal originating in a chamber cannot be reliably considered to be the exclusive representation of activity in that chamber. Several factors are responsible for this, including the details of implant lead placement, an inherent disparity of signal amplitudes, and other reasons.
A particular problem is the problem of “crosstalk” between chambers, that is, the interpretation of a signal not originating in a chamber as a signal that has originated in the chamber. Most commonly, this crosstalk is characterized by the misinterpretation of an electrical signal arising in a ventricle as an atrial signal, through detection of the signal in the atrial IEGM. When this happens, the resultant electrotherapy errors may be both errors of commission and omission. This crosstalk is also referred to as “far field” interference, as it is indicative of “far field” electrical activity.
From the prior art techniques known to the inventors of the present invention, this misinterpretation of signals due to crosstalk has been reduced by using a blanking technique, whereby a signal channel (usually an atrial signal channel) is desensitized during a portion of a cardiac cycle when the crosstalk interference could occur. The unfortunate consequence of this technique is the fact that legitimate signals originating during the blanking period in the chamber in which the signal is blanked are simply not observed, and cannot be acted upon. This compounds the difficulty of properly interpreting the conditions in the heart and particularly in the chamber in which the signal has been blanked.
A more advanced technique is disclosed in U.S. Pat. No. 4,799,486. U.S. Pat. No. 4,799,486 discloses a method and an apparatus for suppressing the ventricular component from an atrial sensing lead used with a dual chamber cardiac pacer, thus obviating the need for an atrial sense refractory period to prevent oversensing of the ventricular interference. The apparatus according to U.S. Pat. No. 4,799,486 utilizes an adaptive filter embodying the Widrow-Hoff least mean square (LMS) algorithm which is connected to receive signals from an endocardial lead having a bipolar ventricular electrode and a unipolar atrial electrode. The bipolar electrodes disposed in the ventricle are connected as the “input” Xk signal to the LMS adaptive filter while the unipolar atrial electrode output is connected as the “desired” or reference signal dk. In accordance with the LMS algorithm, the “error” signal is fed back and used to adjust the tap weights of the adaptive linear filter until the output thereof closely approximates the “desired” signal and then the “error” signal becomes a good approximation of the atrial signal alone, without the ventricular depolarization signal.
The apparatus according to U.S. Pat. No. 4,799,486 does require a considerable amount of the limited resources, in particular energy resources provided by an implantable medical device.
Therefore the object of the present invention is to provide a method and device where interchamber interference, and, particularly, ventricle to atrium crosstalk interference, can be significantly reduced while allowing full-time observation of chamber signals, particularly, atrial chamber signals, thereby only requiring minimized resources.